1. Field of the Invention
This invention relates to improvements in thermoplastic nylon composite sheets useful in forming stamped articles, to a method for forming such sheets and to components thereof.
2. Description of the Prior Art
Composite thermoplastic sheets, such as sheets formed of polyamides, for example, polyepsiloncaprolactam which is also known as nylon 6, have heretofore been utilized to provide smooth-surfaced stamped articles which have the requisite mechanical properties to be utilized in automotive and other applications. Exemplary of such composite sheets and processes for forming the same as those disclosed in U.S. Pat. Nos. 3,931,094 to Segal et al., 3,920,879 to Segal et al., 4,015,039 to Segal et al., as well as U.S. Application Ser. No. 616,732 filed Sept. 25, 1975 to Degginger et al. Typical of such compositions, such as is described in the aforementioned U.S. application (which is expressly incorporated herein by reference) is a composition formed of (a) at least one layer comprising from about 40 to 70 weight percent of polyepsiloncaprolactam, about 0 to 50 weight percent of a particulate filler, and about 0 to 35 weight percent of short glass fibers and (b) a reinforcing layer adjoining layer (a) and comprising from about 60 to 95 weight percent of polyepsiloncaprolactam, about 5 to 40 weight percent of a long glass fiber mat and about 0 to 40 weight percent of a particulate filler.
In forming such sheets, typically the first layer is extruded, the second layer (absent the fiber glass) is also extruded and both such layers, together with the long glass mat positioned between the layers, are laminated together while the resin of the second layer is still in a molten condition.
Although the above-described composites in general have the desired physical properties and surface smoothness, at times the reinforcing layer provides a less than desired reinforcement to the composite. It will be desirable if the reinforcing properties of the composite sheet were less variable.